Hydraulic device with rotor seal

ABSTRACT

In an improved hydraulic device the leakage of fluid between a rotor and a first one of a pair of end plates is prevented by a metal-to-metal seal between the rotor and end plate. To maintain the seal, the rotor and end plate are urged together under the influence of high pressure fluid. In one embodiment of the invention, an annular seal formed of a ultrahigh molecular weight polyethylene is disposed on a side of the rotor opposite from the metal-to-metal seal. The annular rotor seal cooperates with a second end plate to form a cavity in which high pressure fluid is trapped to press the rotor firmly against the first end plate. In a second embodiment of the invention the seal is located on the opposite side of the first end plate from the rotor and cooperates with a fixed surface to form a cavity in which fluid under pressure is trapped. This relatively high pressure fluid presses the first end plate firmly against the rotor.

United States Patent 1 White, Jr.

HYDRAULIC DEVICE WITH ROTOR SEAL Hollis N. White, .lr., West Lafayette, 1nd.

Assignee: TRW Inc., Cleveland, Ohio Filed: Mar. 22, 1974 Appl. No.: 453,710

Inventor:

Int. Cl...... F011: 19/08; F030 3/00; F04c 15/00 Field of Search 418/61 B, 131, 133, 142

[56] References Cited UNITED STATES PATENTS 6/1908 Lechner 418/142 11/1971 White "418/61 B 6/1972 Kolbe et a1. 418/61 B 1/1973 Kolbe et a1. 418/133 Primary Examiner-John .l. Vrablik 1 1 July 15, 1975 [57] ABSTRACT In an improved hydraulic device the leakage of fluid between a rotor and a first one of a pair of end plates is prevented by a metal-to-metal seal between the rotor and end plate. To maintain the seal, the rotor and end plate are urged together under the influence of high pressure fluid. In one embodiment of the invention, an annular seal formed of a ultrahigh molecular weight polyethylene is disposed on a side of the rotor opposite from the metal-to-metal seal. The annular rotor seal cooperates with a second end plate to form a cavity in which high pressure fluid is trapped to press the rotor firmly against the first end plate. In a second embodiment of the invention the seal is located on the opposite side of the first end plate from the rotor and cooperates with a fixed surface to form a cavity in which fluid under pressure is trapped. This relatively high pressure fluid presses the first end plate firmly against the rotor.

2 Claims, 5 Drawing Figures 200 I20/ I p Fin-L. 8

HYDRAULIC DEVICE WITH ROTOR SEAL BACKGROUND OF THE INVENTION The present invention relates to gerotor type devices which are capable of being operated as pumps and as motors.

There are many known gerotor type devices which are capable of being utilized as pumps and as motors. Some of these known gerotor type devices are disclosed in US. Pat. Nos. 3,601,513; 3,289,602; and 3,452,680. Upon testing of a gerotor device constructed in a manner similar to that disclosed in these patents, it was noticed that when the device was utilized as a hydraulic motor, leakage around the rotor decreased as the pressure increased. Thus, the leakage was less when a pressure 3,000 psi was being ported to the motor than when fluid at 2,000 psi was being ported to the motor. It was theorized that the leakage resulted from deflection of a wear plate which is disposed in abutting engagement with the rotor. It is believed that the increased fluid pressure caused the wear plate to deflect against the rotor to restrict leakage between the wear plate and an end surface or side of the rotor.

SUMMARY OF THE PRESENT INVENTION The present invention is drawn to a hydraulic device in which a surface on a rotor and an end plate are urged into tight metal-to-metal sealing engagement under the influence of fluid pressure. This seal between the rotor and end plate retards the leakage of fluid around the rotor to thereby increase the operating efficiency of the associated hydraulic device. In one specific embodiment of the invention, an annular seal is provided on an end of the rotor opposite from the metal-to-metal seal. This annular seal cooperates with an associated end plate to form a cavity which holds high pressure fluid. The fluid pressure forces against the end surface of the rotor urge the opposite end surface of the rotor into metal-to-metal sealing engagement with the associated end plate. To prevent excessive wear and deterioration of the annular seal during operation of the hydraulic device, the annular seal is advantageously formed of a ultrahigh molecular weight polyethylene.

In another embodiment of the invention, the use of a nonmetallic seal between the rotor and one of the end plates is eliminated by providing a pair of plates adjacent to one end of the rotor. An annular seal is mounted between these two plates to form a cavity which is connected in communication with a source of high pressure fluid. The high pressure fluid presses one of the plates firmly against the rotor to form a metal-tometal seal between the plate and the rotor.

Accordingly, it is an object of this invention to provide a new and improved hydraulic device having a rotor and an end plate which are urged into sealing engagement under the influence of fluid pressure forces to reduce leakage between the rotor and end plate.

Another object of this invention is to provide a new and improved hydraulic device having a rotor with a side seal made out of ultrahigh molecular weight polyethylene.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects and features of the present invention will become more apparent upon a consideration of the following description taken in connection with the accompanying drawings wherein:

FIG. 1 is a sectional view of a hydraulic device constructed in accordance with the present invention;

FIG. 2 is an enlarged sectional view of a portion of the hydraulic device of FIG. 1 and illustrating the relationship between a rotor, side seal, and end plate;

FIG. 3 is a sectional view, taken generally along the line 3-3 of FIG. 1;

FIG. 4 is a fragmentary sectional view of a hydraulic device forming a second embodiment of the invention; and

FIG. 5 is an enlarged section view of a portion of the hydraulic device of FIG. 4 and illustrating the relationship between a rotor and end plate assembly.

DESCRIPTION OF SPECIFIC EMBODIMENTS OF THE INVENTION Although it is contemplated that the present invention can be utilized in gerotor type hydraulic devices having many different constructions, the invention is disclosed herein as embodied in a hydraulic device indicated generally by the reference numeral 10 in FIG. 1. The hydraulic device 10 comprises a housing 11 and a cylindrical casing 12 which extends axially from the housing 11 to enclose a stack-up of parts retained in assembly within the body 11 and the casing 12 by means of a plurality of bolts 13. Each of the bolts 13 comprises a threaded shank 14 received in a correspondingly threaded bore 16 formed in an end wall 17 of the housing 11. A cover plate 18 closes an end of the device 10 and a pair of O-ring members 19 and 20 form seals between the housing ll, the casing 12 and the cover plate 18.

Disposed within the casing 12 is a pair of fluid displacement members of a gerotor gear set which during the operation thereof form contracting and expanding fluid pockets for pumping chambers. The gerotor gear set may be more particularly characterized as comprising an internally lobed or toothed metallic stator 21 and an externally toothed metallic star or rotor 22. The stator 21 comprises a cylindrical peripheral wall 23 spaced radially from an inner wall 24 of the casing 12 to provide an annular space or passageway 26 therebetween. During relative movement between the rotor 22 and stator 21 in one direction, the passageway 26 is filled with fluid at a relatively high pressure.

The stator 21 is centrally apertured to provide an inner wall 27 in which there are formed recesses 28 (FIG. 3) in radially angularly spaced relation. In each recess there is disposed a cylindrical vane 29, the vanes together comprising the internal lobes or teeth of the stator 21. Spaces 30 between the vanes 29 comprise the fluid pockets or chambers which alternately expand and contract upon operation of the rotor 22 to provide fluid influx and deflux. At any given time, some of the pockets 30 contain fluid at a relatively high pressure and the other of the pockets 30 contain fluid at a relatively low pressure.

The rotor 22 comprises a plurality of lobes or teeth 31 which in number equal one less than the number of teeth 29 of the statorZI. Wall sections 32 (FIG. 3) which interconnect pairs of adjacent teeth 31 correspond in curvature generally with the outer surfaces of the teeth 29.

The axis of the rotor 22 is offset with respect to the axis of the stator 2I such that movement of the rotor 22 with respect to the stator 21 is simultaneously rotational and orbital, as will be understood by those skilled in the art.

A work input-output shaft 15 is journalled for rotation in the housing 11 about an axis which is aligned with the stationary axis of the stator 21. The shaft 15 is adapted for connection to a motor or the like when the device is being utilized as a pump, and to a driven member such as a wheel or the like when the device 10 is being utilized as a hydraulic motor. The shaft is connected to the rotor 22 by means of a wobble shaft indicated generally at reference numeral 33. The wobble shaft 33 has a longitudinal axis which is disposed at an angle to the axis of the work input-output shaft 15.

In order to drivingly interconnect the shaft 15 and the rotor 22, a pair of spline connections indicated generally at reference numerals 37 and 38 are provided adjacent upper ends of the shaft 33. The spline connection 37 comprises a series of male teeth formed on the shaft 33 and a complemental series of female teeth formed on the rotor 22. The male teeth formed on the shaft 33 are curved in an axial direction to accommodate conical movement of the wobble shaft 33 and thus the spline connections 37 and 38 are conveniently referred to herein as coniflex spline connections.

In order to direct fluid to and from the fluid pockets 30 in timed relation to the orbital and rotational movement of the rotor 22 with respect to the stator 21, the hydraulic device 10 includes a commutation valving arrangement indicated generally at reference numeral 43 (FIG. 1).

More particularly, the arrangement 43 comprises a pair of stationary metal valve plates 44 and 46 which may be referred to, respectively, as an intermediate plate and a manifold plate.

The commutation valving arrangement 43 further comprises a movable commutator valve plate 47 radially surrounded by the stationary plate 46 and situated between the stationary valve plate 44 and a manifold plate 48. A metal clamping plate or end plate 49 is located at the opposite end of the stator 21 and rotor 22 and, by virtue of the bolts 13, the clamping plate 49, the stator 21, the valve or end plate 44, the manifold plate 46, the adjacent plate 48 and the cover plate 18 are connected in fixed assembly with the housing 11 and the casing 12. The annular passageway 26 extends immediately adjacent the inner wall 24 of the casing 12 from the cover plate 18 to the end wall 17 of the housing 11. Other flow passageways are provided by bores 50 and 51 formed in the wobble shaft 33 and by bores 52 and 53 formed in a tubular extension 54 of the work input-output shaft 15.

During operation of the hydraulic device 10 as a motor, fluid chambers 30 are in communication with pressurized fluid in the passage 26 and are expanded as a consequence of the resultant orbital and rotational movement of the rotor 22, whereas the flow chambers 30 which are not in direct communication with the pressurized fluid are reduced in size as a consequence of the movement of the rotor 22. The plates 44 and 49 are connected with axially opposite ends of the stator 21 and cooperate with the stator as end plates of a chamber in which the rotor 22 rotates and orbits during operation of the hydraulic device 10.

The relatively low pressure fluid which is discharged from the contracting pockets 30 is directed through the associated radial passages 56 formed in the intermediate plate 44 and then through a recess formed in the commutator valve plate 47. From the recess in the plate 47 the fluid flows into the passageway 50 formed in the wobble shaft 33, thence through the radial passage 51 formed in the wobble shaft 33 and the radial passage 52 formed in the tubular extension 54 of the drive shaft 33 and thence through the fluid opening 78 formed in the housing 11.

As will be understood by those skilled in the art one end 83 of the wobble shaft 33 which is connected to the input-output shaft 15 rotates only, whereas an opposite end 84 which is connected to the rotor 22 both rotates and orbits in synchronism with the identical movement of the rotor 22. In the embodiment illustrated, the stator 21 has seven lobes or teeth 29, whereas the rotor 22 has six teeth. Thus, for each revolution thereof, the rotor 22 will move through an orbital path of travel six times. The wobble shaft 33 also orbits or moves through a conical path of travel about the end 33 thereof at the orbital speed of the rotor 22.

Since the commutator valve plate 47 is coupled to the nose 60 of the wobble shaft 33, it is also orbited at the orbital speed of the rotor 22 and alternately and sequentially communicates the passageways with chamber 81 surrounding valve plate 47 as it orbits in timed relation to the orbital movement of the rotor 22, whereby the fluid pockets or chambers 30 sequentially and alternately expand under the driving force of the pressurized fluid and then contract to express the fluid therefrom. Since the wobble shaft 33 is coupled to the work input-output shaft 15, it rotates the shaft 15 at the rotational speed of the rotor 22. Operation of the hydraulic device 10 and rotation of the shaft 15 will continue as long as fluid opening 77 commutates with a source of pressurized fluid.

In order to reverse the direction of rotation of the shaft 15, it is only necessary to connect the fluid opening 78 to the source of pressurized fluid and the fluid opening 77 to the low pressure side of the fluid circuitry. The pressurized fluid will then flow through the hydraulic device 10 in a direction opposite to that described hereinabove.

When the hydraulic device 10 is being utilized as a hydraulic pump, the shaft 15 is connected for rotation to any suitable driving motor and fluid will be pumped through the device 10 between the fluid openings 77 and 78 in a direction which depends upon the direction of rotation of the shaft 15. When fluid at a relatively low pressure is supplied at the opening 78 and the device 10 is operating as a pump, high pressure fluid is discharged from the pockets to the commutation valve assembly 43. The high pressure fluid flows from the commutation valve arrangement 43 to the passage 26 and the opening 77.

The hydraulic device 10 is constructed and operated in substantially the same manner as the hydraulic device disclosed in U.S. Pat. No. 3,606,601. To avoid prolixity of description, the disclosure of U.S. Pat. No. 3,606,601 is to be considered as being incorporated herein in its entirety by this reference thereto.

In accordance with the present invention, and in the embodiment of FIG. 1, an annular seal is disposed in an annular groove 102 (see FIGS. 2 and 3) formed in a side surface 104 of the rotor 31. The seal 100 projects out of the groove 102 into sealing engagement with a flat surface 106 of the stationary plate 44. The plate 44 cooperates with the stator 21 and the seal 100 slides on the plate 44 as the rotor 22 orbits and rotates relative to the stator 21.

The seal 100 includes a generally triangular shaped body portion 116 which is disposed within the groove 102. A generally rectangular outer end portion 118 of the seal blocks the clearance space between the surfaces 104 and 106.

The seal 100 blocks the flow of relatively high pressure fluid from the pockets 30 through a clearance space to the central portion of the rotor which is exposed to fluid at relatively low return or drain pressure. Thus, the portion of the side surface 104 which is disposed radially outwardly of the seal 100, that is the lower portion as viewed in FIG. 2, is exposed to relatively high fluid pressure which is equal to the fluid pressure of the associated pocket 30. This relatively high fluid pressure is indicated schematically by the relatively long arrows in FIG. 2. The radially outer portion of the rotor side surface 104, that is the upper portion as viewed in FIG. 2, is exposed to the relatively low drain pressure indicated schematically by the short arrows in FIG. 2. The seal 100 blocks fluid flow from the high pressure side of the rotor 22 to the low pressure side of the rotor 22. Therefore, an annular cavity 110 is formed by the seal 100, rotor surface 104, and plate surface 106.

A side surface 122 (see FIG. 1) of the rotor 22 is pressed into metal-to-metal sealing engagement with the end plate 49 by the fluid pressure in the cavity 110. Thus, the fluid pressure force against the side surface 104 of the rotor 22 urges the opposite side surface 122 of the rotor against the end plate 49. The leakage of fluid around the side surfaces 104 and 122 of the rotor 22 is blocked by the combined influence of the seal 100 and fluid pressure pressing the rotor surface 122 into sealing engagement with the plate 49. It should be noted that even though the seal 100 is spaced from the rotor surface 122 and end plate 49, it enables high pressure fluid to press the rotor 22 against the end plate to block leakage of high pressure fluid from the pockets 30 to the low pressure outlet 78.

During continued use of the hydraulic device 10, the seal 100 is subjected to wear due to sliding movement of the seal relative to the surface 106 of the valve plate 44. In addition, the seal 100 may tend to deteriorate under the influence of hydraulic fluid. To provide a long service life, the seal 100 is made of ultrahigh molecular weight polyethylene. This ultrahigh molecular weight polyethylene has a molecular weight of 2.8 X l, a specific gravity of 0.936 and a density of 0.034 pounds per cubic inch. This ultrahigh molecular weight polyethylene is commercially available from Sparta Manufacturing Company, a division of United States Ceramic Title Company of Dover, Ohio, under the tradename ofUltraspar."

In the embodiment of the invention illustrated in FIGS. l-3, the seal 100 is disposed between the rotor 22 and the end or valve plate 44 to form a cavity 110 in which fluid under pressure urges the rotor into metal-to-metal sealing engagement with the opposite end plate 49. Although the seal 100 is made of ultrahigh molecular weight polyethylene and will therefore have a relatively long service life, the use of a seal between the rotor 22 and end plate 44 may, under certain operating conditions, be objectional. Therefore in the embodiment of the invention illustrated in FIGS. 4 and 5, a seal between a pair of stationary plates forms a cavity which holds fluid under pressure which forces one of the plates into tight metal-to-metal sealing engagement with an end surface of the rotor. Since many of the components of the hydraulic device 200 illustrated in FIGS. 4 and 5 have the same construction and cooperate in the same manner as do the components of the hydraulic device 10 of FIG. 1, similar numerals will be utilized to designate similar components, the suffix letter a being associated with the components of FIGS. 4 and 5 to avoid confusion.

The hydraulic device 200 includes a housing 11a and a cylindrical casing 12a which hold a stack up of parts retained within the body 11a by means of a plurality of bolts 13a. Each of the bolts incudes a threaded shank which is received in a correspondingly threaded bore in an end wall of the housing lla.

Disposed within the casing 12a is a pair of fluid displacement members of a gerotor gear set which during operation thereof form contracting and expanding fluid pockets for pumping chambers. The gerotor gear set includes an internally lobed or toothed metallic stator 21a and an externally toothed metallic star or rotor 22a. The stator 210 includes a peripheral outer surface 23a spaced radially from an inner wall of the casing 12a to provide an annular space or passage 26a therebetween. During relative movement between the rotor 22a and stator 21a in one direction, the passageway 26a is filled with fluid at a relatively high pressure.

The stator 21a, like the stator 21 of FIG. 3, is centrally apertured to receive vanes which form the internal lobes or teeth of the stator. Spaces 30a between the vanes comprise fluid pockets or chambers which alternately expand and contract upon orbital and rotational movement of the rotor 220 relative to the stator 21a to provide fluid influx and deflux. At any given time, some of the pockets 30a contain fluid at a relatively high pressure and the other pockets 30a contain fluid at a relatively low pressure. The axis of the rotor 22a is offset with respect to the axis of the stator 21a since the movement of the rotor 22a with respect to the stator 21a is simultaneously rotational and orbital.

A work input or output shaft 15a has a cylindrical inner end portion, only part of which is shown in FIG. 4. The outer end portion of the shaft is adapted for connection to a motor or the like when the hydraulic device 200 is being utilized as a pump and to be a driven member such as a wheel or the like when the hydraulic device 200 is being utilized as a motor. The shaft 15a is connected with the rotor 22a by means of a wobble shaft 33a. The wobble shaft 330 has a longitudinal axis which is disposed at an acute angle to the axis of the work input-output shaft 150.

During operation of the hydraulic device 200, fluid is directed to and from the pockets 30a in timed relationship with orbital and rotational movement of the rotor 22a with respect to the stator 21a. To provide for this timed relationship between movement of the rotor 22a and the directing of hydraulic fluid, a commutation valve arrangement, a portion of which is shown in FIG. 4 and is designated by the numeral 43a, cooperates with the rotor 22a in a manner generally similar to that explained in connection with the commutation valve arrangement of the embodiment of the invention illustrated in FIGS. 1-3. Therefore, the operation of the commutation valve arrangement 43a will not be further described herein to avoid prolixity of description.

In accordance with a feature of the present invention, an end or clamping plate assembly 210 is associated with the rotor 22a. The plate assembly 210 includes a pair of stationary end plates 212 and 214 which are disposed between the stator 21a and the housing lla.

To prevent the leakage of fluid between an inner surface 218 of the end plate 214 and an end surface 122a of the rotor 22a, the fluid pressure cavity 222 is formed between the two end plates 212 and 214 in the manner shown in FIG. 5. The fluid pressure cavity 222 has a generally annular configuration and includes an annular ring portion 224 which is connected in fluid communication with the fluid passage 26a by a radially extending passage 228. The high pressure flow of fluid from the annular cavity 222 to a low pressure passage area 232 around the wobble shaft 33a is blocked by an annular shaft 236.

The annular seal 236 may have many different configurations. However, in the embodiment of the invention illustrated in FIG. 5, the annular seal 236 has the same configuration as the seal 100. The annular seal 236 is disposed within an annular groove 240 in the inner end plate 214. The seal 236 extends into sealing engagement with a flat annular inner surface 244 of the outer end plate 212. Therefore, the seal 236 cooperates with the two end plates 212 and 214 to block the flow of fluid from the cavity 224 to the relatively low pressure area 232.

During operation of the hydraulic device 200, there is a relatively high pressure fluid force against an annular outer surface 250 of the inner end plate 214. This fluid pressure force is indicated by relatively long arrows in FIG. and presses the end plate 214 into metalto-metal sealing engagement with the end surface 1220 of the rotor 220. In addition, the relatively high fluid pressure forces in the cavity 222 causes an opposite end surface 104a on the rotor 22a to be pressed into tight metal-to-metal sealing engagement with the opposite end plate 44a.

In view of the foregoing description, it can be seen that the hydraulic devices and 200 both include rotors 22, 22a and end plates which are urged into metalto-metal sealing contact to prevent a leakage of high pressure fluid between the rotor and end plates to a passage containing fluid at a relatively low pressure. In the embodiment of the invention illustrated in FIGS. 1-3, the seal 100 cooperates with the end plate 44 to form a cavity 110 in which high pressure fluid urges the rotor 22 firmly against the end plate 49 to provide a metal-to-metal seal between the end surface 122 of the rotor 22 and the end plate 49. This prevents high pressure fluid from leaking from the pockets between the rotor 22 and end plate 49 to the relatively low pressure internal passage. In the embodiment of the invention illustrated in FIGS. 4 and 5, an annular seal 236 cooperates with a pair of plates 212 and 214 to form an annular cavity or chamber 222 in which high pressure fluid from a passage 26a forces the end plate 214 into firm metal-to-metal sealing engagement with the end surface 1220 of the rotor 22a. In addition, the high pressure fluid against the end plate 214 urges the opposite end surface 104 of the rotor 22a into metal-tometal sealing engagement with the end plate 44a.

Having described specific preferred embodiments of the invention, the following is claimed:

1. A hydraulic device comprising a housing internally toothed stator fixedly connected with said housing and having an internal surface partially defining a chamber,

first and second end plate means connected with axially opposite ends of said stator and cooperating with said stator to further define said chamber,

an externally toothed rotor circumscribed by said stator and disposed in said chamber between said end plate means, said rotor having one tooth less than said stator and being movable in an orbit in said chamber about the central axis of said stator during rotational movement of said rotor about its own central axis, said rotor cooperating with said stator and said end plate means during said rotary and orbital movement to define a plurality of pockets some of which contain fluid at a relatively low pressure and other of which contain fluid at a relatively high pressure,

said first end plate means including first and second plate members having first major sides disposed in a side-by-side relationship, said first plate member having a second major side disposed in abutting engagement with said housing, said second plate member having a second major side disposed in abutting engagement with said stator and with said rotor, said first and second plate members having internal surface means defining coaxial central openings disposed in a coaxial relationship with said stator,

a rotatable member supported in said housing for rotation about an axis which is coincident with the central axis of said stator,

shaft means extending through said central openings in said first and second plate members and having a first portion connected with said rotor for common orbital and rotary movement therewith, said shaft means having a second portion connected with said rotatable member for imparting rotary movement to said rotatable member during rotational movement of said rotor in said chamber,

means defining a first passage continuously connected in fluid communication with said pockets containing fluid at a relatively high pressure during operation of said hydraulic device,

means defining a second passage connected in fluid communication with said pockets containing fluid at a relatively low pressure, said second passage being connected in fluid communication with said central openings in said first and second plate members,

said rotor being effective during its orbital and rotational movement relative to said stator to enable fluid to flow through said pockets between said first and second passages, and

means for providing a continuous fluid pressure force between said plate members for continuously urging said rotor and said second plate member into tight abutting engagement during operation of said hydraulic device to restrict fluid flow along a path disposed between said rotor and said second major side surface of said second plate member, said means for providing said fluid pressure force between said plate members to urge said rotor and said second plate member into tight abutting engagement including,

first surface means defining a first annular recess in said first major side of one of said plate members,

said first annular recess opening outwardly toward said first major side surface of the other one of said plate members and circumscribing said shaft means at a location radially outwardly of the central opening in said one plate member, apart to thereby press said second major side sursecond surface means defining a second annular reface of said second plate member against said rocess in the first major side of said one of said plate tor, and members at a location radially outwardly of said seal means disposed in said first annular recess in said first annular recess, said second annular recess one plate member and sealingly engaging the first opening outwardly toward said first major side surmajor side surface of said other plate member for face of the other one of said plate members, enabling the first major sides of said first and secthird surface means defining a radially extending re 0nd plate members to be exposed to high pressure cess in the first major side of said one of said plate fluid radially outwardly of said seal means and for members, said radially extending recess opening preventing a flow of high pressure fluid across said outwardly toward said first major side surface of first annular recess to the central openings in said the other one of said plate members and being conplate members. nected in continuous fluid communication with 2. A hydraulic device as set forth in claim 1 wherein said first passage and said second annular recess for said seal means is formed of ultrahigh molecular weight continuously conducting high pressure fluid from polyethylene. said first passage to said second annular recess dur- 

1. A hydraulic device comprising a housing internally toothed stator fixedly connected with said housing and having an internal surface partially defining a chamber, first and second end plate means connected with axially opposite ends of said stator and cooperating with said stator to further define said chamber, an externally toothed rotor circumscribed by said stator and disposed in said chamber between said end plate means, said rotor having one tooth less than said stator and being movable in an orbit in said chamber about the central axis of said stator during rotational movement of said rotor about its own central axis, said rotor cooperating with said stator and said end plate means during said rotary and orbital movement to define a plurality of pockets some of which contain fluid at a relatively low pressure and other of which contain fluid at a relatively high pressure, said first end plate means including first and second plate members having first major sides disposed in a side-by-side relationship, said first plate member having a second major side disposed in abutting engagement with said housing, said second plate member having a second major side disposed in abutting engagement with said stator and with said rotor, said first and second plate members having internal surface means defining coaxial central openings disposed in a coaxial relationship with said stator, a rotatable member supported in said housing for rotation about an axis which is coincident with the central axis of said stator, shaft means extending through said central openings in said first and second plate members and having a first portion connected with said rotor for common orbital and rotary movement therewith, said shaft means having a second portion connected with said rotatable member for imparting rotary movement to said rotatable member during rotational movement of said rotor in said chamber, means defining a first passage continuously connected in fluid communication with said pockets containing fluid at a relatively high pressure during operation of said hydraulic device, means defining a second passage connected in fluid communication with said pockets containing fluid at a relatively low Pressure, said second passage being connected in fluid communication with said central openings in said first and second plate members, said rotor being effective during its orbital and rotational movement relative to said stator to enable fluid to flow through said pockets between said first and second passages, and means for providing a continuous fluid pressure force between said plate members for continuously urging said rotor and said second plate member into tight abutting engagement during operation of said hydraulic device to restrict fluid flow along a path disposed between said rotor and said second major side surface of said second plate member, said means for providing said fluid pressure force between said plate members to urge said rotor and said second plate member into tight abutting engagement including, first surface means defining a first annular recess in said first major side of one of said plate members, said first annular recess opening outwardly toward said first major side surface of the other one of said plate members and circumscribing said shaft means at a location radially outwardly of the central opening in said one plate member, second surface means defining a second annular recess in the first major side of said one of said plate members at a location radially outwardly of said first annular recess, said second annular recess opening outwardly toward said first major side surface of the other one of said plate members, third surface means defining a radially extending recess in the first major side of said one of said plate members, said radially extending recess opening outwardly toward said first major side surface of the other one of said plate members and being connected in continuous fluid communication with said first passage and said second annular recess for continuously conducting high pressure fluid from said first passage to said second annular recess during operation of said hydraulic device to apply a continuous fluid pressure force to said first major side surfaces of said first and second plate members urging said first and second plate members axially apart to thereby press said second major side surface of said second plate member against said rotor, and seal means disposed in said first annular recess in said one plate member and sealingly engaging the first major side surface of said other plate member for enabling the first major sides of said first and second plate members to be exposed to high pressure fluid radially outwardly of said seal means and for preventing a flow of high pressure fluid across said first annular recess to the central openings in said plate members.
 2. A hydraulic device as set forth in claim 1 wherein said seal means is formed of ultrahigh molecular weight polyethylene. 